The present invention relates to a novel polypeptide that binds selectively to mouse or rabbit immunoglobulin G. More specifically, the present invention relates to a polypeptide that binds to mouse or rabbit immunoglobulin G, a polynucleotide encoding the polypeptide, an expression vector comprising the polynucleotide, a transformant introduced with the expression vector, a method of producing the polypeptide using the transformant, and a composition for immunoassay comprising the polypeptide. The novel peptide according to the present invention binds specifically to mouse or rabbit immunoglobulin G, can replace conventional expensive secondary immunoglobulin G, and can be used in various biological immunoassays. In addition, a conjugate of the polypeptide of the present invention and immunoglobulin G is useful for fabrication of various immunosensors/immunochips and for drug screening.